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Counter shafting and Putties.

movement is leftward, and the final position is that at B. The
radius of curvature should be three to five times the pulley
width.

Countershafting and Speed Cones.—Fig. 539 shews
how a shop machine M may be driven so as to be started and
stopped without affecting the main shaft revolutions or removing
the speed cone belt c c. B is the main shaft and A the counter-
shaft, the latter having fast and loose pullies L and F. The fork/
on the striking bar s then grasps the advancing'side of the belt,
and is moved to right or left by pulling the handles D, which act
on the belt crank L.

Quick return is obtained by the belting at Fig. 538. An open
strap turns the advancing, and a crossed strap the returning pulley,
and in each case there is a narrow fast pulley and a broad loose
pulley. The fork is shifted automatically at either end of stroke,
and the machine stopped by placing both belts in position shewn,
from the handle H. The total width of pullies may be reduced
to four times belt width by the arrangement shewn below, where
two striking bars are employed with which the black tappets
only engage at certain times. Many belt examples will be found
in Part I.

Problems in Belt Driving.—The more difficult cases are
solved in Fig. 540, and will be understood if it be remembered
that the advancing side of the belt must lie at right angles to the
shaft, while the retreating side may make any deviation.

Pullies for Belt Driving are usually split, for convenience
in fixing. Fig. 541 shews the construction of a cast iron, and
Fig. 542 of a wrought iron pulley. The former should have
curved arms if more than 12" diameter (see p. 67), and the latter
is adopted for lightness with high speeds or large pullies. Fig. 543
shews a section through a pair of fast and loose countershaft
pullies, which need not be split.

(7.) Cotton-Rope Gearing is much in favour for spinning
and weaving mills, and has been successfully applied to travelling
cranes and dynamo driving. For mills, the flywheel rim has the
section shewn in Fig. 544, and the ropes lie in wedge grooves.

With a flat pulley thie resistance to slip would be P/i, but in
the grooved pulley shewn the resistance is 2 R/u, there being two